1. Field of the Invention
The present invention relates to a method of covering a substrate surface with a sintered layer, particularly to a method of covering the surface of a steel material with a sintered layer exhibiting a high corrosion resistance and a high abrasion resistance.
2. Description of the Related Art
FIGS. 9 and 10 show conventional methods of covering a substrate surface with a sintered body. In the art shown in FIG. 9, a sintered body 101 prepared by sintering a molded material is bonded to a substrate 102. On the other hand, the art shown in FIG. 10 utilizes a hot isostatic pressing (HIP) which comprises a hermetic welding step applied to a raw material powder loaded in a space defined by a vessel 110 and a substrate 111, and a deaeration step in preparation for the subsequent bonding step which is carried out by means of sintering under pressure so as to cover the substrate 111 with a sintered layer 112.
However, the art shown in FIG. 9 necessitates two heating steps, i.e., the sintering step and the bonding step, leading to a high manufacturing cost. In addition, a precision processing is required for improving the areal precision of the bonding portion between the sintered body 101 and the substrate 102. Thus, this prior art is not applicable to a substrate of a complex shape. The art shown in FIG. 10 also leaves room for further improvement. First of all, this art requires both a hermetic welding step and a deaeration step, leading to an increase in the required time of the manufacturing process, Also, deformation under high temperatures and high pressures is involved in this prior art, with the result that the hermetically welded portion tends to be broken. Further, this art necessitates a welding technique of a high level and a deformation estimating technique of a high level for the substrate during sintering. In practice, a preliminary test is conducted and the amount of deformation is empirically determined based on the result of the preliminary test. Particularly, where the thickness of the substrate is changed from portion to portion in a complex manner, the amount of deformation is large, with the result that the necessity of the preliminary test is enhanced. What should also be noted is that the prior art shown in FIG. 10 requires a very expensive HIP apparatus of high temperature and high pressure.